<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>执行上下文</title>
</head>
<body>
  <script>
    var a=1
    function a(a){
      console.log(a)
    }
    a(2)//报错a不是函数相等于以下函数
    /* 
      var a
      function a(a){
        console.log(a)
      }
      a=1
      a(2)
    */
  </script>
</body>
</html>